Biology Reference
In-Depth Information
of the full-length membrane-spanning components lagging well behind. Impor-
tantly, the T3SS has provided a new area of investigation for antibiotic devel-
opment, as well as potential new antigens for vaccine therapies targeting the
significant global pathogens that necessarily encode a T3SS. Nonetheless, sev-
eral important questions remain unanswered:
Firstly, the source of energy for T3S is still unclear. It has been shown that
the role of the T3SS-associated ATPase likely involves dissociation of effec-
tor proteins from their cognate chaperones, facilitating effective secretion,
while at the same time the proton-motive force has been shown to be inte-
gral to secretion. How these independent processes energize the system in a
concerted manner so that effectors are secreted and translocated though the
injectisome remains to be understood at the molecular level ( Minamino et al.,
2008a ) although the suggestive evolutionary similarity to the F/V/A-ATPases
hints at a related mechanism of transmembrane transport.
l
Secondly, the details of injectisome assembly and substrate switching pro-
cesses require further investigation. In particular, the precise roles of the rod,
ruler, and various secretion apparatus components are subject to controversy
( Erhardt et al., 2010 ). In many cases, it is very possible that different systems
(as well as the flagellum) utilize different mechanisms, which would explain
the difficulty to reconcile all the data into a single unified model.
l
Finally, the translocation of the type 3 effector proteins across mammalian
cell membrane remains very poorly characterized. In particular, recent evi-
dence has challenged the dogma of a continuous channel from the bacterial
cytoplasm to the mammalian cytoplasm. Instead, it has been proposed that
effectors are secreted in the media, and that components of the translocon
allow them to enter the mammalian cell independently of the needle complex
( Edgren et al., 2012 ). These two models are not mutually exclusive, and could
possibly reflect variations in effectors, species, and systems.
l
REFERENCES
Adler, B., Sasakawa, C., Tobe, T., Makino, S., Komatsu, K., Yoshikawa, M., 1989. A dual transcrip-
tional activation system for the 230 kb plasmid genes coding for virulence-associated antigens
of Shigella lexneri . Mol. Microbiol. 3 (5), 627-635 .
Agrain, C., Callebaut, I., Journet, L., et al., 2005. Characterization of a type 3 secretion substrate
speciicity switch (T3S4) domain in YscP from Yersinia enterocolitica . Mol. Microbiol. 56 (1),
54-67 .
Akeda, Y., Galan, J.E., 2005. Chaperone release and unfolding of substrates in type 3 secretion.
Nature 437 (7060), 911-915 .
Allen-Vercoe, E., Toh, M.C., Waddell, B., Ho, H., DeVinney, R., 2005. A carboxy-terminal domain
of Tir from enterohemorrhagic Escherichia coli O157:H7 (EHEC O157:H7) required for
eficient type 3 secretion. FEMS Microbiol. Lett. 243 (2), 355-364 .
Antunes, L.C., Ferreira, R.B., Buckner, M.M., Finlay, B.B., 2010. Quorum sensing in bacterial
virulence. Microbiology 156 (Pt 8), 2271-2282 .
Search WWH ::




Custom Search